Method and device for storing and dosing a reducing agent

ABSTRACT

Apparatus for storing and metering of reducing agents that may be used within the framework of a catalytic exhaust gas aftertreatment, having a device ( 10 ) for storing the reducing agent to be metered and a metering device ( 20 ) for applying the reducing agent to the exhaust gas to be treated, the device ( 10 ) for storing the reducing agent having an outer container ( 11 ) and a cartridge ( 12 ), containing the reducing agent, that is able to be exchangeably positioned in it.

[0001] The present invention relates to an apparatus and a method forstoring and metering a reducing agent according to the definition of thespecies in claims 1 and 10, respectively. The present invention alsorelates to a device for storing a reducing agent according to thedefinition of the species in claim 12.

BACKGROUND INFORMATION

[0002] As a result of steadily lower applicable pollution limits inrecent years, numerous devices and methods have been developed for theaftertreatment of exhaust gases of internal combustion engines.Efficient exhaust gas aftertreatment systems have become available, forinstance, using catalytic converter systems which use ammonia-containingreducing agents for the conversion of NO_(x).

[0003] In order to achieve a reduction of Holding attachment componentsin exhaust gases, reduction catalytic converters have been developed,particularly for Diesel engines. In this respect, the distinction isusually made between so-called SCR systems (in English, selectivecatalytic reduction) and so-called catalytic converters with hydrocarbontrap. On SCR catalytic converters, the nitrogen oxides react selectivelywith a reducing agent. The NO_(x) reduction takes place continuously atthe temperature operating range of the catalytic converter. Ammonia isthe reducing agent having the highest selectivity. In a motor vehicle,for example, ammonia may be obtained from urea, whereas catalyticconverters having a hydrocarbon trap, for example, store NO_(x) asnitrate, and are periodically regenerated in so-called exhaust gas-richphases, using hydrocarbons carried along with the fuel of the internalcombustion engine.

[0004] A system is known from EP-A-0381236 in which, by means ofcompressed air, a urea-water solution for the removal of nitrogen oxidesis metered into the exhaust gases coming from a Diesel engine. However,in this instance, the urea-water solution must first be converted by anadditional chemical process into ammonia, whereby the efficiency of themethod is made worse, and undesired by-products cannot be excluded.

[0005] It is also known within the framework of SCR technology, that onecan use ammonia-containing starting materials, such as ammoniumcarbonate or even ammonia water. However, it is common to all methodsthat ammonia is not used directly, on account of the difficulty ofhandling it.

[0006] Further disadvantages that show up in using ammonia-containingstarting materials are, for instance, relatively low mass-relatedreducing performance, and possibly a limited usefulness in wintertime,whereby appropriate additional measures become necessary.

[0007] Devices and methods for the catalytic reduction of emissions ofinternal combustion engines are known from U.S. Pat. No. 6,122,909.Among other things, it is mentioned here that, within the framework ofSCR methods, ammonia may be added to the exhaust gases so that it mayreact with nitrogen oxides to form nitrogen and water when a catalyticconverter is switched on. However, it should be stated as fact, in thisconnection, that ammonia is a poisonous gas, and that the use of ammoniain SCR systems is connected with great expenditure.

[0008] For this reason, the present invention attempts to make possible,in the most non-expenditure-related manner, the direct use of ammonia,or other reducing agents that have so far been difficult to handle,within the framework of SCR methods.

[0009] This aim is attained using a device and a method having thefeatures of claim 1.

[0010] Because of the use, now possible because of the presentinvention, of pure ammonia, for example, as the reducing agent in SCRmethods, higher efficiencies are achieved as compared to the usualvariants of such methods, by-products are avoided and an increasedmass-related reducing performance is realized.

[0011] The solution according to the present invention permits a veryuser-friendly refilling of the reducing agent, and makes possiblelogistics that are easy to implement.

SUMMARY OF THE INVENTION

[0012] Advantageous embodiments of the method according to the presentinvention and the apparatus according to the present invention are thesubject matter of the dependent claims.

[0013] According to one preferred specific embodiment of the presentinvention, the ammonia is stocked in exchangeable cartridges. Thecartridge has a safety valve which is able to open automatically whenthe cartridge is inserted into its position in its surrounding andholding container. Providing such a safety valve makes possible aparticularly safe insertion and an especially simple exchange ofcartridges.

[0014] Expediently, the container and/or the cartridge are designed aspressure container and safety container. Typical pressures to betolerated are up to 60 bar or even higher, so that the provision ofappropriate pressure containers ensure the safety of the system.

[0015] It further proves expedient to provide a safety closure on thecartridge in addition to the safety valve. This, for example, may bebrought into the released state before being mounted in the container,using a manual rotation, another direction of movement also beingconceivable. Even an automatic rotation is conceivable, e.g. when theartridge is inserted into the container.

[0016] According to one preferred specific embodiment of the deviceaccording to the present invention, the container has a cover wherebythe cartridge may be fixed in its position inside the container, orrather, may be able to be secured. Such a cover may advantageously bedesigned to have a recess on its inner side, into which a holdingattachment of the cartridge may extend. Thus, when the flap is opened,this makes possible a particularly simple pushing in or pulling out ofthe cartridge.

[0017] It is preferred that the container and/or the cartridge are ableto be heated, especially that they may be able to have engine coolingwater applied to them. The container may, for example, be designed tohave hollow walls into which engine cooling water may be brought. Usingthis measure, it is possible, for example, to heat the cartridge and itscontents to a suitable temperature, such as 60° C., 40° C. or even 0°C., (60° C. is preferred for making constant pressure ratios possible),whereby the transportation of reducing agent, particularly ammonia, issupported between the cartridge and the metering device, at least a partof the reducing agent being convertible into the gaseous state with theaid of heating, so that gaseous metering can be carried out. However,another temperature is conceivable which leads to a positive pressureratio.

[0018] It is preferred if the storage device and the metering devicecommunicate with each other via a line for transporting reducing agent,that can be monitored using a pressure sensor. Metering the reducingagent may be carried out either as liquid metering or gas metering, oreven as liquid-gas metering. Using the pressure sensor, an expedientlyset constant system pressure, such as 1.8 bar, is simply made in a waythat is able to be checked. In the case of liquid metering, the reducingagent reaches the metering unit at the pressure prevailing in thecartridge and the container. This is on condition that the meteredquantity has to be corrected as a function of the prevailing pressure. Apressure sensor may also be used to monitor this system pressure.

[0019] The line connecting the storage device and the metering device toeach other expediently has a double wall, and if necessary is filled upusing insulating means.

[0020] The metering device is also expediently able to have enginecooling water applied to it. In this connection, for example, a meteringvalve used within the framework of the metering device may be designedto have hollow walls into which cooling water may be brought.Alternatively to this, the metering device may also be designed to havecooling means, with the aid of which excessive heat transmission fromthe exhaust gas pipe, on which the metering device is expedientlypositioned, may be compensated for. Expediently, an insulating layer isdesigned to be between the metering device and the exhaust gas pipe.

[0021] It has proven expedient to provide a pressure-reducing valveformed in the outer container or in the cartridge. A pressure-reducingvalve is particularly suitable for converting reducing agent stored inliquid form in the cartridge at least partially, especially completely,into the gaseous state.

[0022] What has proven particularly advantageous is providing a safetyvalve in order to prevent the sudden liberation of the entire quantityof ammonia carried in the motor vehicle in liquid and/or gaseous form,which may become life-threatening especially during an accident.Thereby, particularly situations are avoided in which ammonia inconcentrated form is carried into the environment, which would lead todangerous accumulations of poisonous and flammable materials.Additionally, the bursting of the pressure container as a result ofexceeding a maximum permissible operating pressure is avoided in areliable way. Such a pressure increase can, for instance, take place ifthe container is heated above the permissible operating temperature incase of a fire. In such situations, if the reducing agent is released ingood time, in small quantities by way of the safety valve, asupercritical pressure increase is reliably avoided, and bursting of thecontainer is excluded.

[0023] According to one preferred specific embodiment of the presentinvention, ammonia is used as the reducing agent. The use of ammoniawithin the framework of a catalytic exhaust gas purification proves tobe particularly effective. With the use of this method according to thepresent invention, a safe handling is made available of this material,regarded usually as being too dangerous for mobile applications.

[0024] A preferred specific embodiment of the present invention shallnow be further explained with reference to the attached drawings. FIG. 1shows a schematic sectional view of a preferred specific embodiment ofthe device according to the present invention.

[0025] Three essential components of the device according to the presentinvention are a storage device for storing the reducing agent used,ammonia in the exemplary embodiment shown, which here are denotedcollectively as 10, a metering device for applying the reducing agentused, here denoted as 20, to the exhaust gases to be purified ortreated, as well as a pressure line connecting components 10 and 20 toeach other, here marked as 30.

[0026] Storage unit 10 has an outer heatable safety container 11, and acartridge 12 that may be introduced into it and exchanged in it. Safetycontainer 11 is designed to have a cover 11 a that is able to swivel, bythe use of which cartridge 12, when inserted, is able to be positionedand fixed in safety container 11. Cover 11 a has a recess 11 b, intowhich, in the locked condition, a holding attachment 12 a of cartridge12 extends, for safety reasons. It is likewise conceivable to use thisfor the guiding and the axial positioning of the cartridge, by theappropriate forming of the inner wall of the container. With the aid ofholding attachment 12 a, insertion or extraction of cartridge 12 fromsafety container 11 is manageable in a simple way.

[0027] Safety container 11 is designed to have hollow walls 11 c, intowhose cavities 11 d engine cooling water is able to be brought forheating the cartridge to about 60° C. Cartridge 12 is designed to have asafety valve 13 and a safety closure 14. Before the introduction of thecartridge into safety container 11, the safety closure is, for instance,able to be unfastened manually using a 90° turn. Opening of the safetyvalve takes place automatically when the cartridge is pushed in into aregion of safety container 11 which is designed as pressure-reducingvalve 15.

[0028] By the opening of safety valve 13, ammonia is able to flow viapressure-reducing valve and pressure line 30 to metering device 20.Metering device 20 is able to be controlled by an appropriate controlunit 21. Similar to safety container 11, metering unit 20 may bedesigned to have hollow walls 20 a, so that metering device 20 is ableto have cooling water applied to it.

[0029] Pressure-reducing valve 15 makes possible the conversion into thegaseous form of the reducing agent which is expediently stored in thecartridge partially in liquid form, whereby gas metering may beimplemented in a simple way. The pressure-reducing valve is used forreducing the pressure, the actual conversion from the liquid to the gasphase taking place via concrete pressure changes and temperaturechanges. For the sake of completeness, one should point out that agaseous proportion is expediently constantly present in the container.In the case of liquid metering (not shown here), the reducing agentreaches the metering unit without the interposition of apressure-reducing valve, via the connecting line at the tank pressureand the cartridge pressure.

[0030] This requires that the metered quantity has to be corrected as afunction of the present pressure. For this purpose, pressure line 30 isexpediently able to be monitored using a pressure sensor 31 to monitorthe system pressure. It is also possible to hold the system pressureconstant via a pressure control. For safety reasons, the pressure linemay be designed to have double walls and to be insulated, if necessary.

[0031] Metering device 20 is permanently mounted on an exhaust gas pipe40, through which the exhaust gas flows that is to be treated. Themetering device may also be mounted on the frame and have a shortmetering line that extends into the exhaust gas pipe. This makes itpossible to prevent thermal stresses. Reducing agent metered by themetering device is introduced into the exhaust gas in gaseous form viaan injection nozzle pipe 41.

[0032] The metering unit is expediently made up of one or more meteringvalves, which may be cooled, if necessary, by engine cooling water, andmay be decoupled from the heat of the exhaust gas pipe by an insulatingflange or an intermediate pipe.

[0033] If necessary, the use of several metering valves and injectionnozzle pipes is possible to improve the thorough mixing of reducingagent, particularly ammonia, with exhaust gas.

[0034] An insulation 23 is expediently provided between metering valve20 and exhaust gas pipe 40, so as to insulate the metering valve fromthe exhaust gas heat.

[0035] It will be seen that the exhaust gas, having had the introducedreducing agent, here ammonia, applied to it, is supplied to a catalyticconverter 43, where catalytic exhaust gas treatment known per se may becarried out. A substantial advantage in using the device according tothe present invention and in carrying out the method according to thepresent invention is that it requires a reduced number of systemcomponents. The device according to the present invention permits auser-friendly filling up of the reducing agent, so that the logisticsfor making available the ammonia are implemented in a simple manner. Thedevice according to the present invention can be used for passenger carsas well as Nkw's. It offers an improved suitability to winterconditions. Furthermore, no by-products are created during ammoniaproduction. One need not fear any functional disturbances on account ofreducing agent precipitations.

[0036] The storage device according to the present invention is designedas a system made up of a cartridge and a safety container. The safetycontainer may be designed to be pressure-proof so as to further increasesafety. The safety container, as was indicated before, may be made inheated or unheated form, engine cooling water being preferably used forheating. In this context, the temperature prevailing in the cartridgeand the container may additionally be regulated.

[0037] The exchange of the cartridges is carried out in that cover 11 a,which is expediently designed as a quick-change cover, is opened, and,using a grip, (the cartridge) is released from its locked position byrotating it, and pulled out. It is also conceivable that the cartridgemay be clicked into place, using a suitable mechanism, and released by alongitudinal motion. While the cartridge is being pulled out, safetyvalve 13 closes. Subsequently, an exchange cartridge may be pushed inand locked, safety valve 13 being automatically opened again during thepushing-in process.

[0038] With respect to the ammonia example, in conclusion, let usdescribe various storage possibilities. When liquid ammonia is madeavailable having a proportion as gas, the pressure prevailing in thecartridge corresponds to the vapor pressure which is a function of thetemperature prevailing in the cartridge. Typical pressure ranges are 1.9bar at −20° C. through 26.1 bar at +60° C.

[0039] As an additional measure, it is possible to heat the cartridge orstorage device to +60° C., for instance, using engine cooling water.Using this measure, it is possible to set the pressure prevailing in thecartridge or the storage device to be constant, for instance, at 26.1bar.

[0040] In the case of storing liquid ammonia not having a proportion asgas, preferably a diaphragm-type accumulator tank is used as thecartridge. In this context, the cartridge pressure is greater than thevapor pressure; as an example, at a system pressure of 46 bar, theammonia is maintained in the liquid phase up to a temperature of 85° C.

[0041]FIG. 2 shows an alternative specific embodiment of storage device10. The same components as in the device illustrated in FIG. 1 arefurnished with the same reference numerals and are not described again.The storage device has a safety valve or rather a (high-pressure) reliefvalve 16. This relief valve 16 is integrated into safety container 11.It is situated next to pressure-reducing valve 15, and, in parallel withthe latter, is connected to safety closure 14. On the side facing awayfrom the safety closure, valve 16 is connected to a line 100, whichopens out into exhaust gas line 40 upstream of catalytic converter 43(the connection of line 100 to exhaust gas line 40 is not shown in FIG.2).

[0042] Relief valve 16 opens when the internal pressure of the cartridgeexceeds the maximum operating pressure of the cartridge, for instance,on account of an outer heating effect. The ammonia flowing out is thenguided into the exhaust gas flow, where it can burn at least partiallyin the region of the catalytic converter. Thereby, the bursting of thecartridge and the safety container as a result of an exceeding of themaximum operating pressure may be excluded. The potential danger relatedto the ammonia blown out by the relief valve is low in comparison to thebursting of the container, since the pressure storage content is onlyemptied gradually and thus a higher dilution of the NH₃ with thesurrounding air can take place.

[0043] Instead of being integrated into the safety container, reliefvalve 16 may also be integrated into the cartridge itself.Alternatively, two or more connected safety containers each having onecartridge may be provided, which are in optimum fashion each providedwith a relief valve 16. The associated lines 100 can open out, in thiscase, separately or via a collective line into exhaust gas line 40.Alternatively, lines 100 may also simply end in the open, so that excessammonia is let out on the road, so as to avoid an emergency situation.

What is claimed is:
 1. An apparatus for storing and metering of reducingagents which are able to be used within the framework of a catalyticexhaust gas aftertreatment, having a device (10) for storing thereducing agent to be metered, and a metering device (20) for applyingthe reducing agent to the exhaust gas to be treated, wherein the device(10) for storing the reducing agent has at least one outer container(11) and a cartridge (12) which is able to be exchangeably positioned inthe latter, and which contains the reducing agent.
 2. The apparatus asrecited in claim 1, wherein the cartridge has a safety valve (13) whichis able to be opened automatically upon the insertion of the cartridge(12) into its position in the container (11).
 3. The apparatus asrecited in one of claims 1 or 2, wherein the container (11) and/or thecartridge (12) are designed to be pressure and safety containers.
 4. Theapparatus as recited in one of the preceding claims, characterized by asafety closure (14) provided on the cartridge (12).
 5. The apparatus asrecited in one of the preceding claims, wherein the container (11) has acover 11 a by the use of which the cartridge (12) is able to be securedto its position inside the container.
 6. The apparatus as recited in oneof the preceding claims, wherein the container (11) and/or the cartridge(12) are able to be heated, particularly are able to have engine coolingwater applied to them.
 7. The apparatus as recited in one of thepreceding claims, wherein the storage unit (10) and the metering device(20) communicate with each other via a line (30) which is especiallyable to be monitored by using a pressure sensor (31), for transportingreducing agent.
 8. The apparatus as recited in one of the precedingclaims, wherein the metering unit (20) is able to have applied to itengine cooling water or another cooling medium, particularly Dieselfuel.
 9. The apparatus as recited in one of the preceding claims,characterized by a pressure-reducing valve (15) provided in the outercontainer (11) or on the cartridge (12).
 10. The apparatus as recited inone of the preceding claims, wherein at least one pressure relief valve(16) is integrated into the device (10).
 11. The apparatus as recited inclaim (10), wherein the pressure relief valve (16) is integrated into atleast one outer container (11).
 12. A method as recited in claim 10 or11, wherein the cartridge (12) is able to be connected to a line (100)via the pressure relief valve (16) for removing excess reducing agent,when a maximum permissible operating pressure of the cartridge isexceeded.
 13. A method for storing and metering a reducing agent usablewithin the framework of a catalytic exhaust gas aftertreatment,characterized by the use of an apparatus recited in one of the precedingclaims.
 14. The method as recited in claim 13, wherein ammonia injecteddirectly into the exhaust gas to be treated is used as the reducingagent.
 15. A device for storing a reducing agent that is able to be usedwithin the framework of a catalytic exhaust gas aftertreatment,characterized by an outer container (11) and a cartridge (12),containing the reducing agent, which is able to be exchangeablypositioned in the former.
 16. The device as recited in claim 15, whereinthe cartridge has a safety valve (13) which is able to be openedautomatically when the cartridge is inserted into its position in thecontainer.
 17. The device as recited in one of claims 15 or 16, whereinthe container (11) and/or the cartridge (12) are formed as pressurecontainer and safety container.
 18. The device as recited in one ofclaims 15 through 17, characterized by a safety closure provided on thecartridge (12).
 19. The device as recited in one of claims 15 through18, wherein the container (11) has a cover (11 a) by which the cartridge(12) is able to be secured at its position inside the container.
 20. Thedevice as recited in one of claims 15 through 19, characterized by atleast one pressure relief valve (16).
 21. The device as recited in claim20, wherein the pressure relief valve (16) is integrated into the atleast one outer container (11).
 22. The device as recited in claim 20 or21, wherein the cartridge (12) is able to be connected to a line (100)via the pressure relief valve (16) for removing excess reducing agent,when a maximum permissible operating pressure of the cartridge isexceeded.